A randomized controlled trial conducted in Alaska examined the efficacy of 2 second-grade modules of the reform-oriented and culturally based Math in a Cultural Context (MCC) teacher training and curriculum. The results show that the "Picking Berries" (representing and measuring) and "Going to Egg Island" (grouping and place value) modules significantly improved students' mathematics performance. The analysis also revealed that the impacts were broad based and significant for most of the subgroups of schools and students examined. (Contains 13 footnotes, 8 tables, and 4 figures.)